This invention relates to an optically variable and machine-readable device for use on security documents, and more particularly, to an optically variable device having a concealed message thereon. The device may be secured to a document, such as a check, money order, or credit card, such that when a duplication attempt is made on digital or analog copiers or printers, a reproduction of the device bears a visible warning message.
It has been estimated that losses at banks and other financial institutions in the United States due to forgery, fraud, and embezzlement amounted to approximately $860 million in 1989. With the increased availability of color copying machines as well as computer-based desktop publishing systems, scanners, and color printers, concern has increased with respect to the possibility of nefarious reproduction of security documents, such as checks and money orders.
Security documents are especially vulnerable to unauthorized reproduction and alteration through the use of optical scanning devices which can input information into a computer desktop publishing system. The desktop publishing system can then output the information to almost any other document.
There have been numerous attempts in the art to incorporate security features or authentication devices into checks and other security documents to deter counterfeiters. For example, Mowry et al, U.S. Pat. Nos. 4,210,346, 4,227,719, and 4,227,720, teach the use of a cancellation phrase, such as "VOID", printed as part of a background pattern on the face of a security document and then hidden from view by a camouflage image. When the document is reproduced on a color copier, limitations of the optical system of the copier cause the cancellation phrase to be visible on the copy.
LaCapria, U.S. Pat. No. 4,066,280, describes a security document that is partially printed with a reflective ink containing a specular reflecting material, such as powdered aluminum. When the document is reproduced on a color copier, the specular reflection from the document cannot be faithfully reproduced on the copy using the toner.
The inability of a color copier system to reproduce specular reflecting materials such as metals has been used by others in attempts to foil counterfeiters. Optically variable devices such as metal foils, prismatic foils, embossed foils, and holographic foils which can be hot stamped onto a security document, have been used. For example, Webster, Jr. et al, U.S. Pat. No. 4,892,385, shows an optically variable authentication device comprising a reflection diffraction grating structure formed as a relief pattern on a document substrate which produces unique optical color properties that cannot be duplicated by color copying machines.
Antes, U.S. Pat. No. 4,568,141, also describes an optical diffraction element for a document which comprises a plurality of adjoining diffraction grating regions having different orientations such that one or more colored patterns are produced as a result of the diffraction of light. The unique patterns function as a visual test for the authenticity of the document.
However, while such optically variable devices may be useful, they do not provide any automatic means of authentication, and the costs of their fabrication and application make them expensive to use for mass produced documents such as checks and money orders. Further, the devices do not provide any visible warning indication to deter persons from attempting to copy the documents.
Accordingly, a need still exists in the art for an inexpensive optically variable device which may be secured to mass produced documents such as checks, money orders, and credit cards which will produce a warning indication to deter counterfeiters who may be using color copying and/or computer-based desktop publishing systems. The need further exists for an optically variable device which will provide automatic authentication of documents.